Components and methods for use in electro-optic displays

ABSTRACT

A front plane laminate useful in the manufacture of electro-optic displays comprises, in order, a light-transmissive electrically-conductive layer, a layer of an electro-optic medium in electrical contact with the electrically-conductive layer, an adhesive layer and a release sheet. This front plane laminate can be prepared as a continuous web, cut to size, the release sheet removed and the laminate laminated to a backplane to form a display. Methods for providing conductive vias through the electro-optic medium and for testing the front plane laminate are also described.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional of copending application Ser. No.11/928,294, filed Oct. 30, 2007 (Publication No. 2008/0054879), which isa divisional of application Ser. No. 11/747,546, filed May 11, 2007 (nowU.S. Pat. No. 7,443,571), which is a continuation of copendingapplication Ser. No. 10/907,065, filed Mar. 18, 2005 (now U.S. Pat. No.7,236,292, issued Jun. 26, 2007), which is itself a divisional ofapplication Ser. No. 10/249,957, filed May 22, 2003 (now U.S. Pat. No.6,982,178, issued Jan. 3, 2006), which is turn claims priority fromApplication Ser. No. 60/319,300, filed Jun. 10, 2002, and fromApplication Ser. No. 60/320,186, filed May 12, 2003. The entire contentsof all United States patents and published applications mentioned aboveand below are herein incorporated by reference.

BACKGROUND OF INVENTION

The present invention relates to processes and components for formingelectro-optic displays. More specifically, this invention relates tosuch processes and components for forming electro-optic displayscontaining an electro-optic medium which is a solid (such displays mayhereinafter for convenience be referred to as “solid electro-opticdisplays”), in the sense that the electro-optic medium has solidexternal surfaces, although the medium may, and often does, haveinternal liquid- or gas-filled spaces, and to methods for assemblingdisplays using such an electro-optic medium. Thus, the term “solidelectro-optic displays” includes encapsulated electrophoretic displays,encapsulated liquid crystal displays, and other types of displaysdiscussed below.

The term “electro-optic”, as applied to a material or a display, is usedherein in its conventional meaning in the imaging art to refer to amaterial having first and second display states differing in at leastone optical property, the material being changed from its first to itssecond display state by application of an electric field to thematerial. Although the optical property is typically color perceptibleto the human eye, it may be another optical property, such as opticaltransmission, reflectance, luminescence or, in the case of displaysintended for machine reading, pseudo-color in the sense of a change inreflectance of electromagnetic wavelengths outside the visible range.

The terms “bistable” and “bistability” are used herein in theirconventional meaning in the art to refer to displays comprising displayelements having first and second display states differing in at leastone optical property, and such that after any given element has beendriven, by means of an addressing pulse of finite duration, to assumeeither its first or second display state, after the addressing pulse hasterminated, that state will persist for at least several times, forexample at least four times, the minimum duration of the addressingpulse required to change the state of the display element. It is shownin published U.S. Patent Application No. 2002/0180687 that someparticle-based electrophoretic displays capable of gray scale are stablenot only in their extreme black and white states but also in theirintermediate gray states, and the same is true of some other types ofelectro-optic displays. This type of display is properly called“multi-stable” rather than bistable, although for convenience the term“bistable” may be used herein to cover both bistable and multi-stabledisplays.

Several types of electro-optic displays are known. One type ofelectro-optic display is a rotating bichromal member type as described,for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761;6,054,071 6,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791(although this type of display is often referred to as a “rotatingbichromal ball” display, the term “rotating bichromal member” ispreferred as more accurate since in some of the patents mentioned abovethe rotating members are not spherical). Such a display uses a largenumber of small bodies (typically spherical or cylindrical) which havetwo or more sections with differing optical characteristics, and aninternal dipole. These bodies are suspended within liquid-filledvacuoles within a matrix, the vacuoles being filled with liquid so thatthe bodies are free to rotate. The appearance of the display is changedto applying an electric field thereto, thus rotating the bodies tovarious positions and varying which of the sections of the bodies isseen through a viewing surface. This type of electro-optic medium istypically bistable.

Another type of electro-optic display uses an electrochromic medium, forexample an electrochromic medium in the form of a nanochromic filmcomprising an electrode formed at least in part from a semi-conductingmetal oxide and a plurality of dye molecules capable of reversible colorchange attached to the electrode; see, for example O'Regan, B., et al.,Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24(March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845.Nanochromic films of this type are also described, for example, in U.S.Pat. No. 6,301,038, International Application Publication No. WO01/27690, and in copending application Ser. No. 10/249,128, filed Mar.18, 2003. This type of medium is also typically bistable.

Another type of electro-optic display, which has been the subject ofintense research and development for a number of years, is theparticle-based electrophoretic display, in which a plurality of chargedparticles move through a suspending fluid under the influence of anelectric field. Electrophoretic displays can have attributes of goodbrightness and contrast, wide viewing angles, state bistability, and lowpower consumption when compared with liquid crystal displays.Nevertheless, problems with the long-term image quality of thesedisplays have prevented their widespread usage. For example, particlesthat make up electrophoretic displays tend to settle, resulting ininadequate service-life for these displays.

Numerous patents and applications assigned to or in the names of theMassachusetts Institute of Technology (MIT) and E Ink Corporation haverecently been published describing encapsulated electrophoretic media.Such encapsulated media comprise numerous small capsules, each of whichitself comprises an internal phase containing electrophoretically-mobileparticles suspended in a liquid suspension medium, and a capsule wallsurrounding the internal phase. Typically, the capsules are themselvesheld within a polymeric binder to form a coherent layer positionedbetween two electrodes. Encapsulated media of this type are described,for example, in U.S. Pat. Nos. 5,930,026; 5,961,804; 6,017,584;6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773;6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564;6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989;6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790;6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182;6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949;6,521,489; 6,531,997; 6,535,197; 6,538,801; and 6,545,291; and U.S.Patent Applications Publication Nos. 2002/0019081; 2002/0021270;2002/0053900; 2002/0060321; 2002/0063661; 2002/0063677; 2002/0090980;2002/0106847; 2002/0113770; 2002/0130832; 2002/0131147; 2002/0145792;2002/0154382, 2002/0171910; 2002/0180687; 2002/0180688; 2002/0185378;2003/0011560; 2003/0011867; 2003/0011868; 2003/0020844; 2003/0025855;2003/0034949; 2003/0038755; and 2003/0053189; and InternationalApplications Publication Nos. WO 99/67678; WO 00/05704; WO 00/20922; WO00/26761; WO 00/38000; WO 00/38001; WO 00/36560; WO 00/67110; WO00/67327; WO 01/07961; and WO 01/08241.

Many of the aforementioned patents and applications recognize that thewalls surrounding the discrete microcapsules in an encapsulatedelectrophoretic medium could be replaced by a continuous phase, thusproducing a so-called polymer-dispersed electrophoretic display in whichthe electrophoretic medium comprises a plurality of discrete droplets ofan electrophoretic fluid and a continuous phase of a polymeric material,and that the discrete droplets of electrophoretic fluid within such apolymer-dispersed electrophoretic display may be regarded as capsules ormicrocapsules even though no discrete capsule membrane is associatedwith each individual droplet; see for example, the aforementioned2002/0131147. Accordingly, for purposes of the present application, suchpolymer-dispersed electrophoretic media are regarded as sub-species ofencapsulated electrophoretic media.

An encapsulated electrophoretic display typically does not suffer fromthe clustering and settling failure mode of traditional electrophoreticdevices and provides further advantages, such as the ability to print orcoat the display on a wide variety of flexible and rigid substrates.(Use of the word “printing” is intended to include all forms of printingand coating, including, but without limitation: pre-metered coatingssuch as patch die coating, slot or extrusion coating, slide or cascadecoating, curtain coating; roll coating such as knife over roll coating,forward and reverse roll coating; gravure coating; dip coating; spraycoating; meniscus coating; spin coating; brush coating; air knifecoating; silk screen printing processes; electrostatic printingprocesses; thermal printing processes; ink jet printing processes; andother similar techniques.) Thus, the resulting display can be flexible.Further, because the display medium can be printed (using a variety ofmethods), the display itself can be made inexpensively.

A related type of electrophoretic display is a so-called “microcellelectrophoretic display”. In a microcell electrophoretic display, thecharged particles and the suspending fluid are not encapsulated withinmicrocapsules but instead are retained within a plurality of cavitiesformed within a carrier medium, typically a polymeric film. See, forexample, International Application Publication No. WO 02/01281, andpublished US Application No. 2002-0075556, both assigned to SipixImaging, Inc.

Although electrophoretic displays are often opaque (since the particlessubstantially block transmission of visible light through the display)and operate in a reflective mode, electrophoretic displays can be madeto operate in a so-called “shutter mode” in which the particles arearranged to move laterally within the display so that the display hasone display state which is substantially opaque and one which islight-transmissive. See, for example, the aforementioned U.S. Pat. Nos.6,130,774 and 6,172,798, and U.S. Pat. Nos. 5,872,552; 6,144,361;6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, whichare similar to electrophoretic displays but rely upon variations inelectric field strength, can operate in a similar mode; see U.S. Pat.No. 4,418,346. Other types of electro-optic displays may also be capableof operating in shutter mode.

Many of the components used in solid electro-optic displays, and themethods used to manufacture such displays, are derived from technologyused in liquid crystal displays (LCD's), which are of course alsoelectro-optic displays, though using a liquid rather than a solidmedium. For example, solid electro-optic displays may make use of anactive matrix backplane comprising an array of transistors or diodes anda corresponding array of pixel electrodes, and a “continuous” frontelectrode (in the sense of an electrode which extends over multiplepixels and typically the whole display) on a transparent substrate,these components being essentially the same as in LCD's. However, themethods used for assembling LCD's cannot be used with solidelectro-optic displays. LCD's are normally assembled by forming thebackplane and front electrode on separate glass substrates, thenadhesively securing these components together leaving a small aperturebetween them, placing the resultant assembly under vacuum, and immersingthe assembly in a bath of the liquid crystal, so that the liquid crystalflows through the aperture between the backplane and the frontelectrode. Finally, with the liquid crystal in place, the aperture issealed to provide the final display.

This LCD assembly process cannot readily be transferred to solidelectro-optic displays. Because the electro-optic material is solid, itmust be present between the backplane and the front electrode beforethese two integers are secured to each other. Furthermore, in contrastto a liquid crystal material, which is simply placed between the frontelectrode and the backplane without being attached to either, a solidelectro-optic medium normally needs to be secured to both; in most casesthe solid electro-optic medium is formed on the front electrode, sincethis is generally easier than forming the medium on thecircuitry-containing backplane, and the front electrode/electro-opticmedium combination is then laminated to the backplane, typically bycovering the entire surface of the electro-optic medium with an adhesiveand laminating under heat, pressure and possibly vacuum.

As discussed in the aforementioned U.S. Pat. No. 6,312,304, themanufacture of solid electro-optic displays also presents problems inthat the optical components (the electro-optic medium) and theelectronic components (in the backplane) have differing performancecriteria. For example, it is desirable for the optical components tooptimize reflectivity, contrast ratio and response time, while it isdesirable for the electronic components to optimize conductivity,voltage-current relationship, and capacitance, or to possess memory,logic, or other higher-order electronic device capabilities. Therefore,a process for manufacturing an optical component may not be ideal formanufacturing an electronic component, and vice versa. For example, aprocess for manufacturing an electronic component can involve processingunder high temperatures. The processing temperature can be in the rangefrom about 300° C. to about 600° C. Subjecting many optical componentsto such high temperatures, however, can be harmful to the opticalcomponents by degrading the electro-optic medium chemically or bycausing mechanical damage.

This patent describes a method of manufacturing an electro-opticaldisplay comprising providing a modulating layer including a firstsubstrate and an electro-optical material provided adjacent the firstsubstrate, the modulating layer being capable of changing a visual stateupon application of an electric field; providing a pixel layercomprising a second substrate, a plurality of pixel electrodes providedon a front surface of the second substrate and a plurality of contactpads provided on a rear surface of the second substrate, each pixelelectrode being connected to a contact pad through a via extendingthrough the second substrate; providing a circuit layer including athird substrate and at least one circuit element; and laminating themodulating layer, the pixel layer, and the circuit layer to form theelectro-optical display.

Electro-optic displays are often costly; for example, the cost of thecolor LCD found in a portable computer is typically a substantialfraction of the entire cost of the computer. As the use of electro-opticdisplays spreads to devices, such as cellular telephones and personaldigital assistants (PDA's), much less costly than portable computers,there is great pressure to reduce the costs of such displays. Theability to form layers of some solid electro-optic media by printingtechniques on flexible substrates, as discussed above, opens up thepossibility of reducing the cost of electro-optic components of displaysby using mass production techniques such as roll-to-roll coating usingcommercial equipment used for the production of coated papers, polymericfilms and similar media. However, such equipment is costly and the areasof electro-optic media presently sold may be insufficient to justifydedicated equipment, so that it may typically be necessary to transportthe coated medium from a commercial coating plant to the plant used forfinal assembly of electro-optic displays without damage to therelatively fragile layer of electro-optic medium.

Also, the prior art methods for final lamination of solid electro-opticdisplays are essentially batch methods in which the electro-opticmedium, the lamination adhesive and the backplane are only broughttogether immediately prior to final assembly, and it is desirable toprovide methods better adapted for mass production.

The present invention seeks to provide electro-optic components of asolid electro-optic display, these components being well adapted formass production. This invention also seeks to provide processes for theassembly of solid electro-optic displays using these components.

The present invention also seeks to provide methods for testingelectro-optic components prior to final assembly of displays.

One practical problem in the manufacture of electro-optic displays,especially flexible displays, is sealing the display to prevent ingressof materials from the environment (and/or, in some cases, egress ofcomponents of the electro-optic medium). For example, organic lightemitting diodes (which may be useful as the electro-optic medium of adisplay) are notoriously sensitive to damage caused in ingress ofatmospheric moisture, and some particle-based electrophoretic media havealso been shown to have some sensitivity to moisture. In another aspect,this invention provides sealed electro-optic displays.

SUMMARY OF THE INVENTION

Accordingly, in one aspect this invention provides an article ofmanufacture (hereinafter sometimes referred to as a “front planelaminate”) comprising, in order:

a light-transmissive electrically-conductive layer;

a layer of a solid electro-optic medium in electrical contact with theelectrically-conductive layer;

an adhesive layer; and

a release sheet.

In such a front plane laminate, the electrically-conductive layer maycomprise a metal oxide, for example indium tin oxide. Although the frontplane laminate may use a solid electro-optic medium of any of theaforementioned types, for example, a rotating bichromal member medium oran electrochromic medium, it is generally preferred that theelectro-optic medium be an electrophoretic medium, desirably anencapsulated electrophoretic medium.

The adhesive layer used in the front plane laminate may be a heatactivated adhesive or a pressure sensitive adhesive, depending upon theconditions under which the front plane laminate is to be laminated to abackplane, as described in more detail below.

A preferred form of the front plane laminate has a connection area wherethe electrically-conductive layer is exposed free from the electro-opticmedium and the adhesive layer. This connection area may be is formed byan aperture extending through the electro-optic medium and the adhesivelayer so that the connection area is surrounded by the electro-opticmedium and the adhesive layer. Desirably, the release sheet does notextend across the connection area. For reasons explained in more detailbelow, a contact pad of electrically-conductive material may be providedoverlying the electrically-conductive layer in the connection area.

The front plane laminate may have a conductive via in electrical contactwith the electrically-conductive layer and extending therefrom throughor past the layer of electro-optic medium and the adhesive layer. Inthis form of front plane laminate, desirably the end of the conductivevia remote from the electrically-conductive layer is not covered by therelease sheet. The conductive via may be formed from a deformablematerial, such as a material comprising conductive particles dispersedin a polymeric matrix. A contact pad of electrically-conductive materialmay be interposed between the electrically-conductive layer and theconductive via.

The release sheet of the front plane laminate may be provided with asecond electrically-conductive layer. This secondelectrically-conductive layer may be provided on either surface of therelease sheet, but will typically be provided on the surface closer tothe electro-optic medium. As described below, this secondelectrically-conductive layer is useful in testing the front planelaminate before its incorporation into a display. Alternatively or inaddition, the front plane laminate may have an auxiliary adhesive layeron the opposed side of the electrically-conductive layer from theelectro-optic medium; an auxiliary release sheet may be providedcovering the auxiliary adhesive layer.

In another aspect this invention provides an second article ofmanufacture (or front plane laminate) comprising, in order: alight-transmissive electrically-conductive layer; a layer of a solidelectro-optic medium in electrical contact with theelectrically-conductive layer; and an adhesive layer. This article ofmanufacture has a connection area wherein the electrically-conductivelayer is exposed free from the electro-optic medium and the adhesivelayer.

In this front plane laminate, the connection area may or may not extendto an edge of the laminate, but the latter is generally preferred, sothat the connection area is formed by an aperture extending through theelectro-optic medium and the adhesive layer so that the connection areais surrounded by the electro-optic medium and the adhesive layer. Thefront plane laminate may further comprise a release sheet disposedadjacent the adhesive layer on the opposed side thereof from the layerof electro-optic medium. The release sheet may not extend across theconnection area. The release sheet may be provided with a secondelectrically-conductive layer. The front plane laminate may furthercomprise a contact pad of electrically-conductive material overlying theelectrically-conductive layer in the connection area; for reasonsexplained below, the presence of such a contact pad in effect provides adesirable area of increased thickness in the electrically-conductivelayer in the connection area. Although this front plane laminate may usea solid electro-optic medium of any of the aforementioned types, it isgenerally preferred that the electro-optic medium be an electrophoreticmedium, desirably an encapsulated electrophoretic medium.

In another aspect, this invention provides a third article ofmanufacture (front plane laminate) comprising, in order: alight-transmissive electrically-conductive layer; a layer of a solidelectro-optic medium in electrical contact with theelectrically-conductive layer; and an adhesive layer. However, the thirdfront plane laminate of the invention further comprises a conductive viain electrical contact with the electrically-conductive layer andextending therefrom through or past the layer of electro-optic mediumand the adhesive layer.

The third front plane laminate of the present invention may furthercomprise a release sheet disposed adjacent the adhesive layer on theopposed side thereof from the layer of electro-optic medium. The end ofthe conductive via remote from the electrically-conductive layer may notbe covered by the release sheet. The conductive via may be formed from adeformable material, for example a material comprising conductiveparticles dispersed in a polymeric matrix. Like the other front planelaminates of the invention, and for the same reasons, the third frontplane laminate may further comprise a contact pad ofelectrically-conductive material overlying the electrically-conductivelayer in the connection area. Although the third front plane laminatemay use a solid electro-optic medium of any of the aforementioned types,it is generally preferred that the electro-optic medium be anelectrophoretic medium, desirably an encapsulated electrophoreticmedium.

The invention also provides an electro-optic display comprising, inorder: a light-transmissive electrically-conductive layer; a layer of asolid electro-optic medium in electrical contact with theelectrically-conductive layer; an adhesive layer; and a backplane havingat least one pixel electrode, such that application of an electricalpotential between the electrically-conductive layer and the pixelelectrode can change the optical state of the electro-optic medium, thebackplane further comprising at least one contact pad electricallyisolated from the at least one pixel electrode. This display furthercomprises at least one conductive via extending from theelectrically-conductive layer through or past the electro-optic mediumand the adhesive layer to the or one of the contact pads.

As already indicated, in this display the conductive via may extendthrough or past the electro-optic medium, but the former arrangement isgenerally preferred, whereby the conductive via extends through theelectro-optic medium and the adhesive layer so that the conductive viais completely surrounded by the electro-optic medium and the adhesivelayer. The conductive via may be formed from a deformable material, forexample a material comprising conductive particles dispersed in apolymeric matrix. Although the display may use a solid electro-opticmedium of any of the aforementioned types, it is generally preferredthat the electro-optic medium be an electrophoretic medium, desirably anencapsulated electrophoretic medium.

The electro-optic display of the present invention may be provided witha protective and/or barrier layer disposed on the opposed side of theelectrically-conductive layer from the electro-optic medium. A layer oftransparent adhesive may be used to secure the protective and/or barrierlayer to the electrically-conductive layer. The electro-optic displaymay have a sealing material disposed around at least part of theperiphery of the layer of electro-optic medium. In one form of such asealed display, a protective and/or barrier layer is provided extendingbeyond the periphery of the electro-optic medium, and a sealing materialis placed around at least part of the periphery of the electro-opticmedium between the protective and/or barrier layer and the backplane.

In another aspect, this invention provides a process for producing asolid electro-optic display. This process comprises providing an articleof manufacture comprising, in order: a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet. The process further comprisesproviding a backplane comprising a plurality of pixel electrodes anddrive means arranged to apply variable potentials to the pixelelectrodes. The process also comprises removing the release sheet fromthe adhesive layer; and contacting the adhesive layer with the backplaneunder conditions effect to cause the adhesive layer to adhere to thebackplane, thereby securing the adhesive layer, layer of electro-opticmedium and electrically-conductive layer to the backplane.

In this process, the contacting of the adhesive layer with the backplaneis desirably effected under about 20 to about 60 percent relativehumidity. As described in more detail below, to prevent problems due toelectrostatic discharge, the process may include applying ionizedparticles to the front plane laminate during at least one of the removalof the release sheet from the adhesive layer and the contacting of theadhesive layer with the backplane.

In this process, the front plane laminate may be provided with aconnection area where the electrically conductive layer is exposed freefrom the electro-optic medium and the adhesive layer, the backplane beprovided with a contact pad electrically isolated from the pixelelectrodes, and the process place the connection area in electricalcontact with the contact pad. The connection area may be formed by anaperture extending through the electro-optic medium and the adhesivelayer and a deformable electrically-conductive material be placed on thecontact pad prior to contacting the adhesive layer with the backplane,so that during the contacting of the adhesive layer with the backplane,the deformable electrically-conductive material enters the aperture andforms a conductive via electrically connecting the contact pad to theelectrically conductive layer. Alternatively, the connection area may beprovided with a conductive via extending from the electricallyconductive layer through the electro-optic medium and the adhesivelayer, and the process place the conductive via in electrical contactwith the contact pad.

The process may include providing a protective and/or barrier layer onthe opposed side of the electrically-conductive layer from theelectro-optic medium. For this purpose, the front plane laminate mayinclude an auxiliary adhesive layer on the opposed side of theelectrically-conductive layer from the electro-optic medium, and theprocess adhere the protective and/or barrier layer to the auxiliaryadhesive layer. The front plane laminate may have an auxiliary releasesheet covering the auxiliary adhesive layer, and the process include astep of removing the auxiliary release sheet from the auxiliary adhesivelayer before the auxiliary adhesive layer is adhered to the protectiveand/or barrier layer.

In this process, the release sheet may be provided with a secondelectrically-conductive layer, and the process include applying betweenthe light-transmissive electrically-conductive layer and the secondelectrically-conductive layer a voltage sufficient to change the opticalstate of the electro-optic medium.

Although this process may use an electro-optic medium of any of theaforementioned types, such as a rotating bichromal member medium or anelectrochromic medium, desirably the electro-optic medium is anelectrophoretic medium, preferably an encapsulated electrophoreticmedium.

In another aspect, this invention provides a process for forming anelectro-optic display. This process comprises:

providing a front assembly comprising, in order, a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; and anadhesive layer;

removing the electro-optic medium and the adhesive layer from a portionof the front assembly, thereby providing a connection area wherein theelectrically-conductive layer is exposed free from the electro-opticmedium and the adhesive layer;

forming a conductive via on the connection area;

providing a backplane comprising at least one pixel electrode and atleast one contact pad electrically isolated from the at least one pixelelectrode; and

laminating the front assembly to the backplane so that the adhesivelayer adheres to the backplane with the electro-optic medium disposedadjacent the at least one pixel electrode and the conductive via inelectrical contact with the at least one contact pad, so that theelectrically-conductive layer is electrically connected to the at leastone contact pad via the conductive via.

In this process, the connection area may be formed by an apertureextending through the electro-optic medium and the adhesive layer sothat the connection area is surrounded by the electro-optic medium andthe adhesive layer. The front assembly may comprise a release sheetdisposed adjacent the adhesive layer on the opposed side thereof fromthe layer of electro-optic medium, and this release sheet be removedfrom the adhesive layer before the front assembly is laminated to thebackplane. When such a release sheet is present, the step of removingthe electro-optic medium and the adhesive layer from a portion of thefront assembly may also include removing the release sheet from aportion of the front assembly, so that the connection area is free fromthe release sheet. The release sheet may provided with a secondelectrically-conductive layer, and the process may include applyingbetween the light-transmissive electrically-conductive layer and thesecond electrically-conductive layer a voltage sufficient to change theoptical state of the electro-optic medium.

In this process of the present invention, the conductive via may beformed from a deformable material, for example a material comprisingconductive particles in a polymeric matrix.

In this process of the invention, the conductive via may be present inthe front assembly prior to the lamination step, or may be formed duringthe lamination step. In the latter case, the material which will formthe conductive via may be placed on the backplane prior to thelamination step, so that formation of the conductive via occurs duringthe lamination of the front assembly to the backplane. For reasonsexplained briefly above and in detail below, the front assembly may havea front contact pad of electrically-conductive material overlying partof the electrically-conductive layer, and the connection area may beformed so as to expose at least part of the front contact pad.

In this process of the present invention, the front assembly may have alayer of transparent adhesive on the opposed side of theelectrically-conductive layer from the electro-optic medium, and asecond release sheet disposed adjacent the layer of transparentadhesive, and the process may include removing the second release sheetfrom the layer of transparent adhesive and laminating the layer oftransparent adhesive to a protective and/or barrier layer. Typically,the removal of the second release sheet and the lamination of the layerof transparent adhesive will be effected after lamination of the frontassembly to the backplane.

In this process of the invention, after lamination of the front assemblyto the backplane, a sealing material may be placed around at least partof the periphery of the front assembly. When the display is providedwith a protective and/or barrier layer as previously described, thisprotective and/or barrier layer may extend beyond the periphery of theelectro-optic medium, and the sealing material be placed around at leastpart of the periphery of the electro-optic medium between the protectiveand/or barrier layer and the backplane.

This invention also provides a further process for forming anelectro-optic display. This further process comprises:

providing a substrate comprising a light-transmissiveelectrically-conductive layer;

coating a solid electro-optic medium over part of the substrate, leavinga connection area of the substrate uncoated;

coating an adhesive layer over the electro-optic medium, leaving theconnection area uncoated, thereby forming a front assembly;

providing a backplane comprising at least one pixel electrode and acontact pad electrically isolated from the at least one pixel electrode;and

laminating the front assembly to the backplane so that the adhesivelayer adheres to the backplane with the electro-optic medium disposedadjacent the at least one pixel electrode and with theelectrically-conductive layer in the connection area in electricalcontact with the contact pad.

This process of the present invention may include placing a releasesheet over the adhesive layer, the release sheet being removed from theadhesive layer before lamination of the front assembly to the backplane.The release sheet may be provided with a second electrically-conductivelayer, and the process may include applying between thelight-transmissive electrically-conductive layer and the secondelectrically-conductive layer a voltage sufficient to change the opticalstate of the electro-optic medium. The process may include placing adeformable electrically-conductive material on the contact pad of thebackplane before laminating the front assembly to the backplane, so thatthe electrically-conductive layer in the connection area is connected tothe contact pad via the deformable electrically-conductive material.

In this process of the present invention, the front assembly may have alayer of transparent adhesive on the opposed side of theelectrically-conductive layer from the electro-optic medium, and arelease sheet disposed adjacent the layer of transparent adhesive, andthe process may include removing the release sheet from the layer oftransparent adhesive and laminating the layer of transparent adhesive toa protective and/or barrier layer. Typically, the removal of the releasesheet and the lamination of the layer of transparent adhesive will beeffected after lamination of the front assembly to the backplane.

In this process of the invention, after lamination of the front assemblyto the backplane, a sealing material may be placed around at least partof the periphery of the front assembly. When the display is providedwith a protective and/or barrier layer as previously described, thisprotective and/or barrier layer may extend beyond the periphery of theelectro-optic medium, and the sealing material may placed around atleast part of the periphery of the electro-optic medium between theprotective and/or barrier layer and the backplane.

In another aspect, this invention provides a (sealed) electro-opticdisplay comprising a backplane comprising at least one pixel electrode;a layer of a solid electro-optic medium disposed adjacent the pixelelectrode; a light-transmissive electrode disposed on the opposed sideof the electro-optic medium from the backplane; a protective and/orbarrier layer disposed on the opposed side of the light-transmissiveelectrode from the electro-optic medium; and a sealing material forpreventing ingress of material from the environment into theelectro-optic medium, the sealing material being disposed along at leastpart of the periphery of the layer of electro-optic medium and extendingfrom the backplane to the protective and/or barrier layer.

In such a sealed electro-optic display, the sealing material may have alateral thickness, measured parallel to the plane of the backplane,which decreases from the backplane to the protective and/or barrierlayer. Alternatively, the protective and/or barrier layer may be smallerthan the layer of electro-optic medium, measured parallel to the planeof the backplane, and the sealing material may extend over a peripheralportion of the layer of electro-optic medium and contact the peripheryof the protective and/or barrier layer. In a further variant of thesealed electro-optic display of the present invention, the protectiveand/or barrier layer may be larger than the layer of electro-opticmedium, measured parallel to the plane of the backplane, and the sealingmaterial extend between the backplane and the peripheral portion of theprotective and/or barrier layer extending beyond the periphery of thelayer of electro-optic medium.

This invention also provides a second (sealed) electro-optic displaycomprising a backplane comprising at least one pixel electrode; a layerof a solid electro-optic medium disposed adjacent the pixel electrode; alight-transmissive electrode disposed on the opposed side of theelectro-optic medium from the backplane; an electrode support disposedon the opposed side of the light-transmissive electrode from theelectro-optic medium, the light-transmissive electrode and electrodesupport being larger than the layer of electro-optic medium, measuredparallel to the plane of the backplane; and a sealing material forpreventing ingress of material from the environment into theelectro-optic medium, the sealing material extending between thebackplane and the peripheral portion of the light-transmissive electrodeextending beyond the periphery of the layer of electro-optic medium.

Finally, this invention provides two methods for testing a solidelectro-optic medium. The first method comprises:

providing an article of manufacture comprising, in order:

a light-transmissive electrically-conductive layer;

a layer of a solid electro-optic medium in electrical contact with theelectrically-conductive layer;

an adhesive layer; and

a release sheet having a second electrically-conductive layer;

applying a potential difference between the two electrically-conductivelayers, thereby forming an image on the medium; and

observing the image thus formed.

The second testing method of the invention comprises:

providing an article of manufacture comprising, in order:

a light-transmissive electrically-conductive layer;

a layer of a solid electro-optic medium in electrical contact with theelectrically-conductive layer;

an adhesive layer; and

a release sheet;

placing a electrostatic charge on the release sheet, thereby forming animage on the medium; and

observing the image thus formed.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the present invention will now be described,though by way of illustration only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic cross-section through a front plane laminate ofthe present invention showing the manner in which the release sheet ispeeled from the laminate prior to incorporation of the laminate into adisplay;

FIG. 2 is a schematic cross-section, similar to that of FIG. 1, througha second front plane laminate of the present invention undergoingtesting;

FIG. 3 is a schematic cross-section, similar to that of FIG. 1, showingthe front plane laminate of FIG. 1 undergoing testing;

FIG. 4 is a schematic side elevation of an apparatus for carrying outthe testing method shown in FIG. 3;

FIGS. 5, 6 and 7 show three views of a practical form of the apparatusshown schematically in FIG. 4;

FIG. 8 is a schematic cross-section, similar to that of FIG. 1, througha third front plane laminate of the invention;

FIG. 9 is a schematic cross-section, similar to those of FIG. 8, througha fourth front plane laminate of the invention;

FIG. 10 is a schematic cross-section showing the front plane laminate ofFIG. 9 being used in an intermediate stage of a process to form a firstelectro-optic display of the present invention;

FIG. 11 is a schematic cross-section showing the final form of the firstelectro-optic display of the present invention;

FIGS. 12 to 17 are schematic cross-sections, similar to that of FIG. 11,showing modified forms of the electro-optic display using differingsealing arrangements;

FIG. 18 is a schematic cross-section through a fifth front planelaminate of the invention, this front plane laminate being shownundergoing testing;

FIG. 19 is a schematic cross-section showing the front plane laminate ofFIG. 18 being laminated to a backplane in a process of the presentinvention;

FIG. 20 is a schematic cross-section through the final electro-opticdisplay produced by the process of which an intermediate stage is shownin FIG. 19; and

FIGS. 21 and 22 are schematic plan views of coating processes forforming front plane laminates of the present invention.

DETAILED DESCRIPTION

As already mentioned, the present invention provides a an article ofmanufacture (hereinafter referred to for convenience as a “front planelaminate” or “FPL”) comprising, in order: a light-transmissiveelectrically-conductive layer; a layer of a solid electro-optic mediumin electrical contact with the electrically-conductive layer; anadhesive layer; and a release sheet.

The light-transmissive electrically-conductive layer of the front planelaminate serves the dual purpose of forming the front electrode of thedisplay which is eventually formed from the front plane laminate, and ofproviding mechanical integrity to the front plane laminate, therebypermitting the front plane laminate to be handled in a manner whichwould or might not be possible with a structure comprising only theelectro-optic medium and the adhesive layers. In principle, theelectrically-conductive layer may be a single layer, provided that thissingle layer has the necessary electrical conductivity and mechanicalproperties; for example, the electrically-conductive layer couldcomprise a relatively thick (about 100-175 μm) layer of a conductivepolymer. However, it is difficult to find a material with the necessarycombination of electrical and mechanical properties, and no filmssuitable for use as such a single electrically-conductive layer appearto be available commercially. Accordingly, at present the preferred formof electrically-conductive layer in fact comprises two layers, namely athin light-transmissive conductive layer, which provides the necessaryelectrical conductivity, and a light-transmissive substrate, whichprovides the mechanical integrity. The light-transmissive substrate ispreferably flexible, in the sense that the substrate can be manuallywrapped around a drum (say) 10 inches (254 mm) in diameter withoutpermanent deformation. The term “light-transmissive” is used herein tomean that the layer thus designated transmits sufficient light to enablean observer, looking through that layer, to observe the change indisplay states of the electro-optic medium, which will be normally beviewed through the electrically-conductive layer and adjacent substrate(if present). The substrate will be typically be a polymeric film, andwill normally have a thickness in the range of about 1 to about 25 mil(25 to 634 μm), preferably about 2 to about 10 mil (51 to 254 μm). Theelectrically-conductive layer is conveniently a thin layer of forexample, aluminum or indium-tin-oxide (ITO), or may be a conductivepolymer. Polyethylene terephthalate (PET) films coated with aluminum orITO are available commercially, for example as “aluminized Mylar”(“Mylar” is a Registered Trade Mark) from E.I. du Pont de Nemours &Company, Wilmington Del., and such commercial materials may be used withgood results in the present invention, either as theelectrically-conductive layer or (with an appropriate coating) as arelease sheet bearing the second electrically-conductive layer.

In a variant of the present invention, a self-supporting solidelectro-optic medium can be prepared starting with a release sheet. Alayer of the electro-optic medium is formed, by coating, printing orotherwise, on the release sheet, and thereafter an adhesive layer isformed over the electro-optic medium (i.e., on the opposed side of theelectro-optic medium from the release sheet). The combined electro-opticmedium and adhesive layer can then be used to apply the electro-opticmedium to any desired substrate, which could a three-dimensional object.If desired, a second layer of adhesive could be applied on the opposedside of the electro-optic medium from the layer first applied, therebyconverting the electro-optic medium into a double-sided adhesive filmwhich could be laminated, for example, to a backplane on one side and toan electrode on the other.

In a presently preferred form of this variant of the invention, amonolayer of capsules of an encapsulated particle-based electrophoreticmedium prepared substantially as described in the aforementioned2002/0185378 (see also the corresponding International ApplicationPCT/US02/15337), Example 7 was deposited on a release sheet, dried, andovercoated with an aqueous urethane binder (NeoRez R-9320, availablefrom NeoResins, 730 Main Street, Wilmington Mass. 01887), which servedto planarize the layer of capsules and form an adhesive layer. Afterdrying the adhesive layer, the combined capsule layer and adhesive layercould be peeled away from the substrate as a self-supporting film.

The front plane laminate of the present invention is well adapted formass production. For example, a roll of a commercial metallized plasticfilm may be converted to the front plane laminate by a roll-to-rollcoating process using conventional commercial coating equipment. Themetallized plastic film is first coated with a slurry of capsules inbinder, as described in application Ser. No. 10/063,803 (now U.S. Pat.No. 6,822,782), and this capsule layer is dried. A layer of adhesive,for example the aforementioned aqueous urethane resin NeoRez R-9320, isthen coated over the capsule layer and dried. The release sheet is thenapplied over the adhesive, and the combined front plane laminate canthen be formed into rolls ready for storage and/or transportation. Whenit is desired to use the front plane laminate in the construction ofdisplays, the laminate can be unrolled and cut into pieces of the sizerequired for individual displays or groups of displays (in some cases,it may be convenient to laminate multiple displays in a single operationand then separate individual displays at a later stage) usingconventional commercial apparatus.

The release sheet used in the front plane laminate of the presentinvention can be of any known type, provided of course that it does notcontain materials which might adversely affect the properties of theelectro-optic medium, and numerous suitable types of release sheet willbe known to those skilled in the art. Typical release sheets comprise asubstrate such as paper or a plastic film coated with a low surfaceenergy material, for example a silicone.

When the front plane laminate of the present invention is used in adisplay, it is of course necessary to make electrical contact with theconductive layer within the laminate, and this it is usually necessaryto provide at least one area (hereinafter called the “connection area”)of the display where the conductive layer is free from the electro-opticmedium; note that the contact area may be coated with an adhesive tosecure the connection area to an appropriate conductor in the finaldisplay, and the adhesive used in the connection area may or may not bethe same adhesive used in the remaining areas of the display where theelectro-optic medium is present. Although the presence of this adhesivedoes introduce additional electrical resistance, the currents requiredby most electro-optic media are so low that the additional resistance isnot a problem, and if necessary conductive adhesives containingconductive particles or fibers of types well known in the art can beused to lower the resistance introduced by the adhesive in theconnection area. Alternatively, as described in more detail below, adeformable conductive material may be used to secure the connection areato the backplane.

A connection area can be provided in two different ways. Firstly, asdescribed below with reference to FIGS. 21 and 22, the formation of thelayer of electro-optic medium can be controlled so as to leave uncoatedareas (“gutters”) where no electro-optic medium is present, and portionsof these uncoated areas can later serve as the connection areas.Alternatively, the whole surface of the laminate can be covered with theelectro-optic medium and this medium later removed from the connectionarea in any convenient manner, for example by mechanical abrasion orchemical degradation of the electro-optic medium. In some cases, afterremoval of the electro-optic medium from the connection area, thelaminate may need cleaning to remove residue from the electro-opticmedium; for example, if the electro-optic medium is an encapsulatedelectrophoretic medium, it is desirable to remove any internal phaseremaining after rupture of the capsules during removal of theelectrophoretic medium from the connection area.

One important advantage of the front plane laminate of the presentinvention is the ability to test the quality of the laminate before itsincorporation into a final display. As is well known to those skilled incoating technology, coated materials of often display imperfections suchas voids, streaks, variation in thickness of coated layers, pointdelamination and other problems which can adversely affect theperformance of the coated material or even render it unusable.Encapsulated electro-optic media also suffer from defects due tobursting of the capsules during coating. Thus, it is usually necessaryto inspect a coated product, either by eye or by a machine visionsystem, to identify any defects before using it in a final product. Thisis especially necessary with electro-optic media intended for use inactive matrix displays, since in practice the cost of the active matrixbackplane of such a display is much greater than the combined cost ofthe electro-optic medium and front electrode structure; if a defectivecoating of electro-optic medium is laminated to a backplane, both themedium and the backplane must be scrapped since there is normally no wayof removing the medium while preserving the backplane.

Unfortunately, the inspection of electro-optic media presents peculiardifficulties as compared with other coated materials. An electro-opticmedium only undergoes its crucial change in optical state when subjectedto an electric field, and several types of coating defects (for example,inclusions or impurities in the adhesive layer or burst capsules) whichadversely affect the ability of the medium to undergo its change inoptical state are very difficult to observe visually. Thus, it isdesirable to able to apply an electric field to the medium duringtesting. However, in most prior art processes this is not possible.Typically, in such prior art processes, a backplane and a frontelectrode structure are formed separately, a layer of electro-opticmedium is provided on one of these components (usually the frontelectrode structure) and the backplane and front electrode structure arelaminated together with the electro-optic medium sandwiched betweenthem. Such a process does not provide any point before the lamination atwhich the electro-optic medium can be switched between its opticalstates, and thus defects in the electro-optic medium or the adhesive maynot be discovered until after the formation of the final display, withresultant costly scrapping of good backplanes which happen to belaminated to defective electro-optic medium or adhesive. (Note that inmost cases, it is not possible to test an electro-optic mediumadequately by simply pressing it mechanically against an electrode,since surface irregularities on the medium or the electrode usuallyrender it impossible to produce a uniform change in the optical state ofthe medium, and such a uniform change in optical state is required forthorough testing of the medium.)

As already indicated the present invention provides methods for testingthe electro-optic medium and other components of the laminate prior tofinal attachment of the laminate to a backplane.

A basic front plane laminate of the present invention, and a process forthe testing thereof will now be described with reference to FIGS. 1 and2.

FIG. 1 is a schematic cross-section through a basic front plane laminateof the present invention showing the manner in which the release sheetis peeled from the laminate prior to incorporation of the laminate intoa display. As shown in FIG. 1, the laminate (generally designated 10)comprises a light transmissive substrate 12, which has the form of atransparent plastic film, conveniently a 7 mil (177 mm) PET sheet.Although not shown in FIG. 1, the substrate 12, the lower surface ofwhich (as illustrated in FIG. 1) forms the viewing surface of the finaldisplay, may have one or more additional layers, for example aprotective layer to absorb ultra-violet radiation, barrier layers toprevent ingress of oxygen or moisture into the final display, andanti-reflection coatings to improve the optical properties of the finaldisplay. The substrate 12 carries a thin light-transmissiveelectrically-conductive layer 14, preferably of ITO, which acts as thefront electrode in the final display.

A layer (generally designated 16) of an electro-optic medium isdeposited upon, and in electrical contact with, the conductive layer 14.The electro-optic medium shown in FIG. 1 is an opposite charge dualparticle encapsulated electrophoretic medium of the type described inthe aforementioned 2002/0185378, and comprises a plurality ofmicrocapsules, each of which comprises a capsule wall 18 containing ahydrocarbon-based liquid 20 in which are suspended negatively chargedwhite particles 22 and positively charged black particles 24. Themicrocapsules are retained within a binder 25. Upon application of anelectrical field across the layer 16, the white particles 22 move to thepositive electrode and the black particles 24 move to the negativeelectrode, so that the layer 16 appears, to an observer viewing thedisplay through the substrate 12, white or black depending upon whetherthe layer 14 is positive or negative relative to the backplane at anypoint within the final display.

The laminate 10 further comprises a layer 26 of lamination adhesivecoated over the electro-optic medium layer 16 and a release layer 28covering the adhesive layer 26. The release layer is conveniently a 7mil (177 mm) PET film, which may be provided with any appropriaterelease coating, for example a silicone coating. As illustrated at theleft side of FIG. 1, the release layer 28 is peeled from the adhesivelayer 26 before the laminate is laminated, by means of the adhesivelayer 26, to a backplane to form the final display.

FIG. 2 shows a modified front plane laminate (generally designated 10′)which is identical to the laminate 10 shown in FIG. 1, except that athin second conductive layer 30, preferably of aluminum, is provided onthe surface of the release layer 28 facing the electrophoretic medium.(The second conductive layer 30 could alternatively be provided on thesurface of the release layer remote from the electrophoretic medium.However, the arrangement shown in FIG. 2 is generally preferred, since,as described below, the second conductive layer 30 is used for testingof the electrophoretic medium, and, to produce as large an electricfield as possible across this medium for any given operating voltage, itis desirable to keep the distance between the two conductive layers assmall as possible.) As already indicated, the release layer 28 andconductive layer 30 can be formed from an aluminized PET film, and suchfilms are readily available commercially. Although not shown in FIG. 2,in some cases, depending upon the properties of the electro-opticmedium, it may be necessary or desirable to provide a coating of a lowsurface energy material, such as a silicone, over the second conductivelayer 30 to prevent this layer sticking to the electro-optic medium.Although this low energy material introduces an additional electricalresistance into the system, the resistance of most electro-optic mediais sufficiently high that the presence of the additional resistance isnot a problem. If necessary, the driving voltage used during testing(see below) may be adjusted to allow for the additional resistance.

FIG. 2 shows the laminate 10′ being tested, with the conductive layer 14grounded and a drive voltage V, sufficient to cause a change in theoptical state of the electro-optic medium and preferably equal to thedrive voltage used in the final display, applied to the secondconductive layer 30. Contact with the second conductive layer 30 may beachieved by peeling a small area of the release layer 28 away from theadhesive layer 26; contact with the conductive layer 14 may be achievedby similar peeling and either removing the electro-optic medium from asmall area of the laminate or by piercing this medium with, for example,crocodile clips. Advantageously, an alternating, preferably square wave,voltage is applied to the second conductive layer 30, so that the entiresheet of laminate 10′ flashes black and white. The human eye is verysensitive to even small areas which do not flash in this situation, sothat even small defects are readily observable. Furthermore, since thetesting method can readily be applied to large sheets of the laminate,in many cases small defects can be marked and subsequent cutting of thelarge sheet into portions needed for individual displays can beadjusted, thus enabling the maximum number of individual displays to beobtained from a sheet with some defects.

The testing method shown in FIG. 2 allows inspection to be achieved withprecise application of a low voltage corresponding to the drive voltageused in the actual display, thus essentially guaranteeing that theproperties of the laminate displayed during testing will correspond tothose achieved in the final display. For example, an area of theelectro-optic medium which does undergo a change of optical state, butmore slowly than required by the design specification, can readily bedetected by this method. The method does not require high voltagesources, which can be hazardous in certain environments, leavesessentially no residual electrostatic charges on the laminate, and iswell adapted for automated inspection.

A preferred embodiment of a second testing method of the invention isillustrated schematically in FIG. 3, which shows the second testingmethod being applied to the laminate 10 shown in FIG. 1. As shown inFIG. 3, the conductive layer 14 is grounded in the same way as in FIG.2. An electrostatic head 32 is disposed near the release layer 28,thereby distributing electrostatic charge on the exposed surface of therelease layer 28; although positive charges are shown in FIG. 3,negative charges could of course be used and indeed, for reasons similarto those already discussed, it is advantageous to apply charges ofopposite polarities in successive steps of the testing process. Theelectrostatic charge placed on the release layer 28 causes the opticalstate of the laminate 10 to change.

FIG. 4 is a more detailed, though still schematic, side elevation of apreferred apparatus (generally designated 40) for carrying out thetesting method of FIG. 3. This apparatus 40 includes a “transparentelectrostatic chuck” (generally designated 42) which is used to hold thelaminate 10 in position for testing. (An electrostatic chuck ispreferred over mechanical clips because an electrostatic chuck ensuresthat the laminate is absolutely flat against the glass support, thuseliminating reflective artifacts in the image seen.) The chuck 42comprises a flat glass plate 44 to which is bonded with optical cement aplastic film 46 (conveniently of PET), the exposed surface of whichcarries an ITO layer 48. A solenoid-actuated pogo pin 50 mounted on thechuck 42 contacts the conductive layer 14 (see FIG. 1) of the laminate10, and a voltage is applied between the conductive layers 14 and 48 toproduce between these layers an electrostatic attraction which holds thelaminate 10 firmly in position on the chuck 42 during testing.

A line scan camera 52 is mounted below the chuck 42 so that it can scanthe laminate 10 through the chuck. An ionographic print head 54 ismounted above the chuck 42 to apply electrostatic charge to the releaselayer 28 (FIG. 1) of the laminate 10 in the manner illustrated in FIG.3. Suitable ionographic print heads, of the type described in U.S. Pat.No. 4,160,257, are available commercially; one experimental apparatusused a head recycled from a Xerox Docuprint 1300 Electron Beam printer,sold commercially by Xerox Corporation, Stamford Conn. The print head 54is provided with a spring-loaded slide mechanism 56 (illustrated in ahighly schematic manner in FIG. 4) which maintains the print head 54 ata constant distance, typically about 0.5 mm, from the exposed surface ofthe release layer 28. The camera 52 and print head 54 are attached to acommon linear motion stage (not shown) and during testing of thelaminate 10 move from left to right in FIG. 4, the camera 52 beingpositioned a short distance “downstream” from the print head 54 so thatthe linear area scanned by the camera 52 is an area which has recentlybeen imaged by the print head 54.

The preferred mode of operation of the apparatus shown in FIG. 4 is asfollows. An operator places the laminate sheet 10 on to theelectrostatic chuck 42. The operator ensures that the sheet is properlyaligned using registration pins or printed registration marks (notshown). After the operator closes a safety interlock cover (not shown),the pin 50 makes electrical contact with the conductive layer 14. Theapparatus then activates the chuck 42, thus causing an electric fieldbetween the two conductive layers 14 and 48 and pulling them together.

The ionographic print head 54 drives the electrophoretic medium to anoptically saturated optical state by projecting a beam of ions onto therelease layer 28. The ions cause the formation of an equal and oppositeimage charge on the conductive layer 14, and the resultant electricfield changes the color on the viewing surface (the lower surface inFIG. 4) of the laminate 10. Over time, the energy stored in the electricfield across the electrophoretic medium dissipates by electricalconduction.

The line scan camera 52 images the laminate 10 through the electrostaticchuck 42. The apparatus is designed to provide precise, evenillumination to the laminate being imaged by the camera. A controller(not shown) controls the various components of the machine (camera,stage, light, etc.) and processes images from the camera 52 to decide ifthe laminate sheet being measured is within manufacturingspecifications. Since it is necessary to detect areas which fail tochange optical state in either direction (i.e., white areas that fail toturn black or black areas that fail to turn white), at least two scansof the laminate 10 are required for full testing, with the polarity ofthe print head 54 being reversed between scans. The controller may use asimple thresholding algorithm to determine location of defects: pixelsof the image that fall outside of an upper and/or lower reflectivitybound for each optical state tested are considered defects. The computermay then perform more sophisticated processing on the resultant pixeldefect data to determine whether the laminate meets specifications. Forexample, a group of contiguous defect pixels might be called a singledefect. The computer could count the number of pixel defects per area,location of each defect, average defect area, and any number of othercomputed parameters.

The apparatus can then indicate if the sheet is accepted or rejected. Ifthe sheet is rejected, the apparatus can generate a numerical controlprogram for a laser cutter to dice the laminate sheet under test intosmaller sheets that meet specifications. Alternatively, rejected sheetscould be discarded.

It should be noted that the voltages which need to be applied to theprint head 54 in such an apparatus are much less than might be thoughtfrom a naïve analysis of the resistance of a typical release layer ascompared with that of an electro-optic medium, and, as alreadyindicated, the print head voltage required in practice is well withinthe capability of commercial ionographic print heads. For example, inone experiment the apparatus illustrated in FIG. 4 was used to testencapsulated electrophoretic media which, in the final displays, were tobe switched between their black and white states using 15V drivingpulses having durations of 150 to 500 msec. In the laminates, therelease layer used was a PET film having a resistance of 10¹³ ohm cm².Considering only the resistance of the electrophoretic medium (about 10⁸ohm cm²) versus the resistance of the release layer one might concludethat driving the ink through the release layer would require over 1million volts. However, the capacitance of the layers was about the same(28 pF/cm² for the electrophoretic medium and 50 pF/cm² for the releaselayer) so in practice, pulses of less than 1000 V across theelectrophoretic medium and release layer combined causedresistance-capacitance spikes across the electrophoretic medium thatcarried sufficient energy for full transitions between the opticalstates thereof.

In experiments using an electrophoretic medium as discussed above with a0.05 mm (2 μm) release layer and the aforementioned Xerox print head,full transitions between black and white states were successfullydemonstrated at a tracking speed of 10 mm/sec. using a driver electrodevoltage of 1900 VPP, a driver electrode frequency of 50 KHz, a driverpulse width of 30 Hz, and spacing of 0.5 mm between the print head andthe release layer. To drive the medium to its white optical state, thecontrol electrode voltage was set to 0 V, the screen electrode voltageto 180 V and the accelerating voltage to +1000 V. To drive the medium toits black optical state, the control electrode voltage was set to 200 V,the screen electrode voltage to 20 V and the accelerating voltage to−1000 V. All voltages given are with respect to a common ground.

FIGS. 5, 6 and 7 are photographs showing the actual apparatus used inthese experiments. FIG. 5 shows the overall test set up, FIG. 6 showsthe print head switching the electrophoretic medium from white to black,and FIG. 7 shows the ionographic print head and its associated controlboard.

This test method of the present invention has been shown to achieve fulloptical state transitions and provides a non-contact testing methodswhich carries no risk of bursting capsules in encapsulated electro-opticmedia and can achieve a high testing speed.

FIG. 8 shows a laminate (generally designated 200) which closelyresembles the laminate 10 shown in FIG. 1, but which is provided with aconnection area having the form of an aperture 202 extending through therelease sheet 28, the adhesive layer 26 and the electro-optic mediumlayer 16, thus exposing an area of the conductive layer 14 lying at thebase of the aperture 202. The aperture 202 may be formed by anyconventional technique, including for example depth routing techniques.The formation of the aperture 202 may be performed in two stages, thefirst of which removes the release sheet 28 and the second of whichremoves the adhesive layer 26 and the electro-optic medium layer 16. Thefirst stage of the process may be carried out by physically cutting therelease sheet 28 using a mechanical cutter provided with a depth controlto limit the depth of cut. The severed portion of the release sheet 28can then be removed, for example by suction from a vacuum device.Alternatively, the release layer could be removed by laser ablation orby dry etching, especially reactive ion etching, which can be performedin a highly controllable and repeatable manner. Etching may also be usedto remove the adhesive layer 26 and the electro-optic medium layer 16,preferably using an etching technique for which the conductive layer 14acts as an etch stop. However, the presently preferred technique forremoving the adhesive layer 26 and the electro-optic medium layer 16 iswet mechanical rubbing; this technique may also be used to remove therelease sheet 28. Such mechanical rubbing is preferably effected using anon-woven and non-shredding tape, such as polyester rayon, and removesthe material by a shearing type action.

The use of high energy material removal techniques, such as laserablation, is not recommended for removal of the layers 26 and 16 sincein practice such high energy techniques tend to damage the conductivelayer 14. As already mentioned, the substrate 12 and conductive layer 14are conveniently formed from an ITO-coated PET film, and such films areavailable commercially. However, in such commercial films, the thicknessof the ITO is only of the order of 100 nm (0.1 μm) and hence the ITO isrelatively easily damaged by high energy removal techniques.

To reduce the risk of damage to the conductive layer 14, it may beadvantageous to increase the thickness of the layer 14 in the area wherethe aperture 202 is to be formed; obviously, it is not practical toincrease the thickness of the whole conductive layer 14, since thislayer lies between an observer and the electro-optic medium layer 16when a display is in use, and increasing the thickness of the wholelayer 14 would adversely affect the optical properties of the display.However, the aperture 202 will typically be formed in a peripheral areaof the display, normally an area which is not visible in use, forexample by being hidden under the bezel of the display, and hence thethickness of the layer 14 can be increased in such an area withoutaffecting the optical performance of the display. The thickness of theconductive layer 14 in the area which will eventually be exposed byaperture 202 may be effected by printing a conductive ink, for example asilver or graphite ink, over the ITO layer; note that in practice theconductive ink is printed over the relevant area of the PET/ITO film (orsimilar film used to form the substrate 12 and conductive layer 14)before the electro-optic medium layer 16 is coated or otherwisedeposited over the conductive layer 14.

Forming an aperture through some electro-optic media may cause theformation of significant amounts of debris. For example, in FIG. 8, a“blank” area from which microcapsules are missing is shown to the leftof aperture 202, and this blank area indicates that one microcapsule hasdisappeared the layer 16 as a result of the formation of aperture 202.(The size of the microcapsules in FIG. 8 is of course greatlyexaggerated relative to the size of the aperture; in practice, a typicalaperture would have a diameter of the order of about 10 microcapsules.)The “missing” microcapsule was punctured during the formation ofaperture 202 and hence formed debris in the aperture. This debris shouldbe removed before the front plane laminate is used in a display, sinceit may interfere with the necessary electrical contact between theconductive layer 14 and the backplane of the display. Some methods forformation of the aperture 202, for example wet mechanical rubbing, maythemselves serve as efficient removers of debris from the electro-opticmedium, but if the method used to form to aperture 202 does not itselfremove debris, any known debris removal technique, for example plasmaetching or washing the aperture with a stream of a liquid or gas, may beused to remove the debris, provided of course that the debris removaltechnique used does not cause damage to the electro-optic medium whichwould result in unacceptable adverse effects on the optical performanceof the final display.

The aperture 202 is, in the final display, filled with a conductivematerial and thus forms a conductive path between the front electrode(the conductive layer 14) and the backplane of the display. (Althoughonly one aperture 202 is shown in FIG. 8, in practice it may beadvantageous to provide more than one aperture within a portion of thefront plane laminate 10 used to form a single display, thus providingmultiple conductive paths between the front electrode and the backplaneof the display and permitting the display to function correctly even ifone conductive path fails to function correctly due to, for example,cracking of a material forming the conductive path.) However, thefilling of the aperture 202 with the conductive material may be effectedbefore, or essentially simultaneously with, the lamination of the frontplane laminate to the backplane.

FIG. 9 illustrates a front plane laminate (generally designated 210) inwhich the filling of the aperture 202 has effected before lamination. InFIG. 9, the aperture 202 shown in FIG. 8 has been filled with aconductive material to form a conductive via 204 extending from theconductive layer 14 to the exposed surface of the release sheet 28. Thevia 204 may be formed from any conductive material, though the use of adeformable conductive material, for example a material comprisingconductive particles in a polymeric matrix, is convenient. Conductivematerials of this type include silver ink, silver-filled epoxy resin,metal-containing silicones and other materials. Alternatively, the via204 could be formed from a conductive tape. The conductive material maybe inserted into the aperture 202 in any convenient manner, for exampleby printing an ink on to the front plane laminate or by injecting theconductive material through a needle into the aperture 202. It should benoted that the use of a process such as printing, which may leave excessconductive material on the surface of the release sheet 28, is notobjectionable since the excess conductive material will be removed withthe release sheet 28 prior to lamination of the front plane laminate tothe backplane. If the conductive material is of a type which requirescuring, partial curing of the conductive material may be effected afterinsertion of the conductive material into the aperture 202, but finalcuring of the conductive material is desirably postponed until afterlamination of the front plane laminate to the backplane in order thatthe conductive material may remain somewhat deformable during thislamination and thus make better electrical contact with the backplane.One advantage of using silver-filled epoxy resin to form the conductivevia 204 is that that material does not require a residence time forcuring prior to lamination; a lamination conducted within a preferredelevated temperature range, as described below, effects curing of thesilver-filled epoxy resin during the lamination itself.

The front plane laminate structures shown in FIGS. 8 and 9 willtypically be formed while the front plane laminate is still in bulk, webform. Next, the front plane laminate will typically be cut into piecesof the size needed to form individual displays. This cutting may beeffected using a laser cutter or a cutting die. It is one of theimportant advantages of the invention that the front plane laminate canbe prepared in the form of a web, which can then be cut into a varietyof different size pieces for use with differing displays; thus, themanufacturer of the front plane laminate does not need to keep a largeinventory of different sized pieces, but can prepare the front planelaminate as a web and cut this web into pieces of varying sizes asorders are received. Again, it should be noted that cutting of sometypes of electro-optic media may result in the formation of debris, forexample from ruptured capsules of an encapsulated electrophoreticmedium, and appropriate cleaning may be required after cutting in orderto remove such debris.

The present invention allows flexibility in the order of performing thevarious steps in the preparation of the front plane laminate. Forexample, instead of removing the release sheet, adhesive layer andelectro-optic medium from parts of a web of front plane laminate (andoptionally inserting a conductive material), and then severing the webto form individual pieces of the laminate, the web could be severedfirst and removal of the various layers effected on the individualpieces of laminate. In this case, it may be desirable to provide a jigor die to hold the pieces of laminate in order to ensure that removal ofthe release layer, adhesive layer and electro-optic medium is effectedfrom accurately defined areas of the pieces of laminate. Othervariations in the order of process steps are of course possible; forexample in producing the laminate of FIG. 9, formation of the apertures202 (FIG. 8) could be effected on a web of laminate, which is thereaftersevered to produce individual pieces, and insertion of the conductivematerial to form the conductive vias could be effected after severing,possibly immediately before lamination of the laminate pieces tobackplanes.

The front plane laminates shown in FIGS. 8 and 9 are desirably tested byone of the methods previously described before being integrated intodisplays as described below with reference to FIGS. 10 to 17.

The next major step in the process for forming an electro-optic displayis laminating the front plane laminate to a backplane. However, beforethe front plane laminates shown in FIGS. 8 and 9 are laminated to abackplane, the release sheet 28 must be removed. This removal may beeffected by applying an adhesive tape to the exposed surface of therelease sheet and peeling the release sheet from the adhesive layerusing the adhesive tape. Alternatively, in some case the release sheetmay be arranged to extend beyond the edge of the adhesive layer 26 andthe electro-optic medium layer 16 (for example by using a release sheetweb which is wider than the applied adhesive layer 26), leaving one ormore “tabs” of release sheet which can be grasped manually and pulled toremove the release sheet. Removing the release sheet 28 exposes theadhesive layer 26 ready for the lamination process.

FIG. 10 illustrates schematically the front plane laminate 210 shown inFIG. 9 being laminated to a backplane 406 provided with pixel electrodes408 and a contact pad 410. FIG. 10 shows a protective layer 412 beinglaminated over the substrate 12 of the front plane laminate 10simultaneously with the lamination of the front plane laminate to thebackplane 406. Although provision of such a protective layer isdesirable for reasons discussed below, the protective layer need not beattached in the same lamination as that used to laminate the front planelaminate to the backplane, and typically the protective layer will beapplied in a second lamination after the front plane laminate has beenlaminated to the backplane. Alternatively, the protective layer 412could be applied to the substrate 12 before the electro-optic medium 16is applied to the substrate. It should be noted that the front planelaminate is inverted in FIG. 10 relative to the position in which it isillustrated in FIG. 9.

FIG. 10 shows the lamination being effected using a roller 414 and amoveable heated stage 416 which, during the lamination process, is movedin the direction of arrow A. The backplane 406 is placed on the stage416, and a cut piece of front plane laminate 210 is placed over thebackplane 406, the front plane laminate 210 and the backplane 406preferably being aligned using pre-positioned alignment referencemarkers, e.g., edge references, to control alignment in both directionsparallel to the plane of stage 416 to achieve precision alignment of thetwo components prior to lamination. Protective layer 412 may then beplaced over front plane laminate 210.

Once aligned, protective layer 412, front plane laminate 210 andbackplane 406 are laminated together by advancing stage 416 in thedirection of arrow A under roller 414, while the stack of material onstage 416 is held at a specific elevated temperature, desirably in therange of 50-150° C., and preferably in the range of 80-110° C. for hotmelt adhesives such as ethylene vinyl acetate. Roller 414 may be heatedor un-heated, and applies a pressure desirably in the range of 0.2 to0.5 MPa and preferably in the range of 0.35 to 0.5 MPa. The laminationadhesive layer is preferably temperature- and pressure-activated, sothat the heat and pressure of the lamination laminate front planelaminate 210 and backplane 406 together as the stack passes under roller414, thus forming an electro-optic display. It will be seen from FIG. 10that the lamination is arranged to that the conductive via 204 contactsthe contact pad 410, while the electro-optic medium becomes disposedadjacent the pixel electrodes 408; it is of course necessary that thecontact pad 410 be electrically isolated from the pixel electrodes 408in order that the potentials applied to the common front electrodeformed by the conductive layer of the front plane laminate and the pixelelectrodes can be varied independently to generate electric fieldsacross the electro-optic medium sufficient to change the optical statethereof.

The lamination process can be varied in numerous ways. For example, thestage 416 could remain stationary and the roller 414 move. Both theroller 414 and the stage 416 could be unheated, and the laminationadhesive pressure-activated by the pressure applied by the roller 414.If the lamination is to be conducted using the front plane laminate ofFIG. 8 rather than that of FIG. 9, a deformable conductive material, forexample a silver-filled epoxy resin, may be printed or otherwisedeposited over the contact pad 410 so that during the lamination thisdeformable conductive material is forced into the aperture 202 (FIG. 8)thus forming a conductive via during the lamination process. Thelamination could of course also be carried out using two rollers (heatedor un-heated) rather than one roller and a stage.

More fundamental variations of the lamination process are also possible.The lamination process shown in FIG. 10 is a “piece-to-piece” process,in which individual cut pieces of front plane laminate are laminated toindividual backplanes. However, the lamination process could also beeffected in a roll-to-roll mode, with a web of front plane laminatebeing laminated to a web comprising multiple backplanes formed on aflexible substrate; such a web might make use of transistors formed frompolymeric semiconductors, as described in certain of the aforementionedE Ink and MIT patents and published applications. Such a roll-to-rolllamination may be effected by passing the two webs through a nip betweena pair of rollers, which may be heated or unheated, depending upon thetype of adhesive used. It will be apparent to those skilled inconducting roll-to-roll processes that in such a roll-to-roll laminationremoval of the release sheet from the front plane laminate could beconducted “in-line” by providing a take-up roller which applies tensionto separate the release sheet from the front plane laminate, and onwhich the separated release sheet is wound. Such a roll-to-rolllamination process is also well-adapted for simultaneous lamination of aprotective layer. Following the roll-to-roll lamination process, thecombined “display” web will of course be cut to produce individualdisplays.

The lamination could also be effected in what may be termed a“web-to-piece” mode, with a continuous web of front plane laminate,stripped of its release sheet, being laminated to a plurality ofbackplanes arranged in an appropriate holder, with the web of frontplane laminate later being cut to produce individual displays.

Care should be exercised in choosing the environmental conditions, suchas relative humidity and temperature, under which the front planelaminate/backplane lamination is affected, since such conditions havebeen shown, at least in the case of encapsulated electrophoreticdisplays, to affect the optical performance of the display produced bythe lamination. For such electrophoretic displays, it is recommendedthat the lamination be effected at 20 to 60 percent relative humidity,optimally at 40 percent relative humidity. Also, for suchelectrophoretic displays, preferably, the lamination process is carriedout at about room temperature, e.g., in the range of 15 to 25° C. Inaddition to relative humidity and temperature, other environmentalparameters are desirably controlled. The lamination process is desirablycarried out in a clean room environment with a low particle count toimprove manufacturing yields. The environment should also beelectrostatic-free. Electrostatic discharge (ESD), which may occur dueto the high generation of static when the release sheet is removed fromthe front plane laminate, may damage the backplane. To reduce the riskof ESD, an ion cannon or gun may be used to spray electricallyneutralizing ionized particles on to the front plane laminate both whilethe front plane laminate is covered with the release sheet and after therelease sheet has been removed and the front plane laminate is placed onthe lamination stage or is being laminated in a roll-to-roll process.The ionized particles serve to discharge or electrically neutralize thefront plane laminate. In addition, the lamination environment should beproperly grounded, including grounding the operators, flooring, etc., tofurther reduce the risk of ESD.

It will be seen from FIG. 10 that after the lamination, even if aprotective film has been applied, at least the edge of the electro-opticmedium is exposed to the environment, and, as previously noted, manyelectro-optic media are susceptible to environmental factors, such asmoisture, oxygen, and particulates. Accordingly, according to thepresent invention, the display may be sealed to prevent adverse effectson the electro-optic medium caused by such environmental factors, thusincreasing the operating life of the display. Examples of useful sealsare illustrated in FIGS. 11 to 17.

FIG. 11 shows a “fillet” edge seal 520. (The pixel electrodes areomitted from FIGS. 11 to 17 for simplicity.) In this type of seal, boththe substrate 12 and the protective layer 412 are of the same size asthe electro-optic medium layer (measured parallel to the plane of thebackplane 406) and the seal 520 is of substantially triangularcross-section, having a lateral thickness, measured parallel to theplane of the backplane 406, which decreases from the backplane 406 tothe protective layer 412. The seal 520 extends from the surface ofbackplane 406 up to, but not past, protective layer 412, as shown inFIG. 11.

The seal 520, and the other seals shown in FIGS. 12 to 17, may be formedby dispensing an appropriate sealing material around the periphery ofthe electro-optic medium using standard dispensing machinery formanufacturing. For example, a conventional robotic needle dispenser maybe used to dispense a seal 520 having a thickness of 0.3 to 0.6 mm and awidth of 0.8 to 1.5 mm. Alternatively, the sealing material may beprinted using standard printing processes, such as silk screening,stenciling, transfer, etc., on either front plane laminate 10 orbackplane 406 before lamination.

The fillet seal 520 shown in FIG. 11 has advantages from a displayprocessing and manufacturing standpoint, as it is easily integrated intothe other steps used for manufacturing the display. The other edge sealgeometries shown in FIGS. 12 to 17 require protective layer 412 (and insome cases, also the substrate 12) to be a different size from the layerof electro-optic medium, and such a size difference may requireadditional processing and/or manufacturing steps, which may complicatethe overall display manufacturing process.

FIG. 12 illustrates an “overlap” seal 522. In this type of seal, theprotective layer 412 is smaller than the layer of electro-optic medium(measured parallel to the plane of the backplane 406) and the sealingmaterial extends over a peripheral portion of the layer of electro-opticmedium and contacts the periphery of the protective layer 412. The seal522 extends from the backplane 406 up to, but not past, protective layer412, as shown in FIG. 12.

FIG. 13 illustrates an “underfill” seal 524. In this type of seal, theprotective layer 412 is larger than the layer of electro-optic medium(measured parallel to the plane of the backplane 406) and the sealingmaterial extends between the backplane 406 and the peripheral portion ofthe protective layer 412 extending beyond the periphery of theelectro-optic medium and the substrate 12.

FIG. 14 illustrates a “true underfill” seal 526. In this type of seal,the protective layer 412, the substrate 12 and (optionally) theconductive layer 14 are all larger than the layer of electro-opticmedium (measured parallel to the plane of the backplane 406), desirablyby a distance of about 0.5 to 1.5 mm. The necessary “overhang” ofprotective layer 412, substrate 12 and conductive layer 14 may beprovided by removing a peripheral portion of the layer of electro-opticmedium from around the periphery of the display prior to the laminationof the front plane laminate 10 or 210 to the backplane 406. Also priorto this lamination, sealing material is dispensed around the peripheryof the display, so that when the backplane 406 and front plane laminate10 are laminated together, the edge seal 526 is formed. Alternatively,the sealing material may be applied after lamination by using capillaryforces or direct pressure to fill the sealant into the small cavityaround the electro-optic medium.

The underfill seals of FIGS. 13 and 14 are advantageous in that theyonly allow for diffusion of environmental factors in one dimension (leftto right in FIGS. 13 and 14) through a substantial thickness of thesealing material before the environmental factors can reach theelectro-optic medium 16. The protective sheet tends to be lesssusceptible to diffusion of environmental factors therethrough than thesealing material, and hence it is desirable to use an underfill sealwhich ensures that such environmental factors must diffuse in onedimension through a substantial thickness of the sealing material beforethey can reach and affect the electro-optic medium, as opposed to a typeof seal which allows these factors to migrate in two dimensions into theelectro-optic medium.

FIG. 15 illustrates a “non-contact overlap” seal 550. This type of sealclosely resembles the overlap seal 522 shown in FIG. 12, but the sealingmaterial does not extend to the edge of the protective film 412, leavinga gap between the sealing material and the protective film. Desirably,as shown in FIG. 15, a flexible sealant 522 is inserted into the gap toimprove the sealing of the electro-optic medium 16. It has been foundempirically that, in the overlap seal 522 of FIG. 12, there is atendency for the sealing material to break away from the edge of theprotective film, because of, for example, differences between thecoefficients of thermal expansion of the various materials used in thedisplay, and the differing degrees to which layers at differingdistances from the backplane are constrained against lateral movementrelative to the backplane. Formation of a break between the adjacentsurfaces of the sealing material and protective film adversely affectsthe sealing of the electro-optic medium and hence the operating lifetimeof the display. The non-contact overlap seal 550 allows for somerelative movement between the sealing material and the protective filmwithout adverse effects on the sealing of the electro-optic medium.

FIG. 16 illustrates an “underfill dam” seal 560. This type of sealclosely resembles the true underfill seal 526 shown in FIG. 14. However,in the underfill dam seal 560, both the electro-optic layer and theconductive layer terminate short of the edge of the substrate 12, thusleaving a peripheral portion of this substrate 12 exposed. Also, theunderfill dam seal 560 includes a protective dam 562. The dam 562 isformed from a curable material, for example an epoxy resin, which isdispensed on to either the backplane 406 or the front plane laminate,and cured before the backplane and the front plane laminate arelaminated together, the dam 562 being positioned so that extends betweenthe backplane 406 and the aforementioned exposed peripheral portion ofthe substrate 12.

FIG. 17 illustrates an “channel” seal 570. This type of seal closelyresembles the underfill dam seal 560 shown in FIG. 16, but uses twospaced beads 572 and 574 which are dispensed and cured prior tolamination of the backplane and front plane laminate to define a channelbetween the two beads. This channel is then filled with the sealingmaterial, but before the lamination step.

In the seals shown in FIGS. 16 and 17, spacer beads may be introducedbetween the backplane and the front plane laminate to prevent extrusion(i.e., squeezing out) of the sealing material during the laminationstep.

In some cases, it may be advantageous to apply an adhesion promoter toeither the front plane laminate and/or the backplane prior toapplication of the sealing material to achieve improved adhesion of thesealing material to the backplane and front plane laminate.

If an edge seal alone does not provide sufficient protection againstenvironmental factors, a barrier tape could also be applied. Such abarrier tape would preferably run around the perimeter of front planelaminate 10 to supplement the barrier properties of the edge seal 510.The barrier tape could be a die cut piece of adhesive backedpolychlorotrifluoroethylene (sold commercially by HoneywellInternational, Inc. under the Registered Trade Mark Aclar), metallizedPET, aluminum, or stainless steel. Similarly, an additional barrier filmmay be applied to the protective film to further enhance protection ofthe display against environmental factors. Similarly, an additionalbarrier film may be applied over the protective film 412 to furtherenhance the environmental integrity of the display.

FIG. 18 shows a further front plane laminate (generally designated 600)of the present invention being tested by a method similar to that ofFIG. 2. The front plane laminate 600 comprises a release sheet 28provided with a conductive layer 30, an adhesive layer 26, anelectro-optic medium layer 16, a conductive layer 14 and a substrate 12,all of which are essentially identical to the corresponding parts of thefront plane laminate 10′ shown in FIG. 2. However, the front planelaminate 600 further comprises an auxiliary adhesive layer 702 on theopposed surface of the substrate 12 from the conductive layer 14, thisauxiliary adhesive layer 702 being formed from a transparent adhesive,and an auxiliary release sheet 704 on the opposed side of adhesive layer702 from the substrate 12. The front plane laminate 600 also comprises acontact pad 706, formed from silver ink, on a peripheral portion ofconductive layer 14. An aperture 708 is formed through release sheet 28adjacent contact pad 706 and the portions of electro-optic medium layer16 and adhesive layer 26 overlying contact pad 706 are removed, so thatcontact pad 706 is accessible from the exposed surface of release sheet28 via aperture 708.

FIG. 18 shows the front plane laminate 600 being tested usingessentially the same process as used in FIG. 2. It will be seen fromFIG. 18 that a peripheral portion 28′ of release sheet extends beyondsubstrate 12, thus leaving an area 30′ of conductive layer 30 exposed.An electrical conductor 710 connects the area 30′ to a voltage source712, which is also connected to a second electrical conductor 714.Conductor 714 passes through aperture 708 and contacts contact pad 706,thus enabling the voltage source 712 to apply a voltage betweenconductive layers 14 and 30 and change the optical state of theelectro-optic medium layer 16.

The front plane laminate 600 may be manufactured by first applying theauxiliary adhesive layer 702 and the auxiliary release sheet 704 to thesubstrate 12 already provided with conductive layer 14; as previouslymentioned, conveniently substrate 12 and conductive layer 14 areconstituted by a commercially available PET/ITO or similar compositefilm. The contact pad 706 is then printed on the exposed surface of theconductive layer 14. Next, the conductive layer 14, including the areaoccupied by contact 706 is coated with the electro-optic medium,followed by the adhesive layer 26, which is in turn covered by therelease sheet 28 provided with the conductive layer 30. Finally, theaperture 708 is formed through the release sheet 28 and the adhesivelayer 26 and the electro-optic medium layer 16 cleaned from the contactpad 706 in any of the ways already described above with reference toFIG. 2. The front plane laminate 600 is now ready for testing asillustrated in FIG. 18.

FIG. 19 illustrates to front plane laminate 600 of FIG. 18 laminated toa backplane 406 provided with pixel electrodes 408 and a contact pad410, all of which are essentially identical to the corresponding partsof the backplane shown in FIG. 10. A conductor 720 formed from anelectrically-conductive adhesive establishes electrical contact betweenthe contact pad 706 of the front plane laminate 600 and the contact pad410 of the backplane 406; this contact pad 410 is of course electricallyisolated from the pixel electrodes 408. To produce the structure shownin FIG. 19, the electrically-conductive adhesive may be printed on tothe contact pad 410, the release sheet 28 removed from the front planelaminate 600, and the backplane and front plane laminate laminatedtogether using any of the techniques previously described.

FIG. 20 shows one form of display (generally designated 800) which canbe prepared from the laminated structure shown in FIG. 19. Tomanufacture the display 800, the auxiliary release sheet 704 is removedfrom the auxiliary adhesive layer, and the front planelaminate/backplane structure (the contact pad 410 and the pixelelectrodes 408 are omitted from FIG. 20 for ease of illustration) isthen laminated to a barrier film 802, which is larger (parallel to theplane of the backplane 406) than the front plane laminate 600. A furtherprotective film 802, preferably a PET film having a thickness of about200 μm, and provided with a laminating adhesive layer, formed of atransparent adhesive, is then laminated to the exposed surface of theprotective film 802. Next, a sealing material 808 is injected into thegap between the backplane 406 and the barrier film 802, thereby forminga type of underfill seal which is similar in principle to the seal 524shown in FIG. 13, except that the sealing material 808 extends from thebackplane 406 to the barrier film 802, rather than to the protectivefilm 412.

Although not shown in the drawings, the backplane 406 is provided withcircuitry which connects the pixel electrodes 408 and the contact pad410 (FIG. 19) to a peripheral portion of the backplane, to which isattached a tape connect package 810 provided with a driver integratedcircuit 812 (which controls the operation of the display); the tapeconnect package 810 is connected to a printed circuit board 814.

The specific displays described above with reference to FIGS. 2 to 20use a front plane laminate having at least one aperture formed throughthe release layer, adhesive layer and layer of electro-optic medium, sothat this aperture is completely surrounded by these layers. However,the use of such apertures is not essential. The release layer, adhesivelayer and layer of electro-optic medium could be removed from an areawhich adjoins the periphery of the front plane laminate, so that the“aperture” has the form of a recess in the edge of the release layer,adhesive layer and layer of electro-optic medium. Alternatively, theexposed area of the conductive layer of the front plane laminate neededfor electrical contact with the backplane may be provided not byremoving the release layer, adhesive layer and layer of electro-opticmedium, but by not coating a specific area of the conductive layer withthese additional layers, as illustrated in FIGS. 21 and 22.

FIG. 21 illustrates a “lane” coating process in which a continuous strip920 of an electro-optic medium is deposited on a web 922, which can formthe substrate of a front plane laminate. Multiple areas of conductivematerial, only two of which are shown in FIG. 9, are provided on the web922, each of these areas having the form of a rectangle 924, which iscompletely covered by the strip 920 of electro-optic medium, and a tab926 extending from the rectangle 924 beyond the edge of the strip 920,so that part of the tab 926 is not covered by the electro-optic medium.Although not shown in FIG. 21, the adhesive layer of the front planelaminate is subsequently coated in the same pattern as the electro-opticmedium, so that in the final web of front plane laminate, part of thetab 926 is free from both electro-optic medium and adhesive layer, sothat there is no need to remove these two layers from a portion of theconductive layer before lamination of the front plane laminate to abackplane.

The exposed tab 926 of conductive material could be directly laminatedto a suitable contact pad on the backplane. However, in general it ispreferred, prior to the lamination, to coat a deformable conductivematerial, such as those previously described, on to the backplane sothat this deformable conductive material lies between the contact pad onthe backplane and the tab 926 to ensure good electrical contact betweenthe contact pad and the tab.

It will be appreciated that considerable variation in the form of theconductive layer is possible in the process shown in FIG. 21. Forexample, the conductive layer could have the form of a continuous stripwith tabs provided at regular intervals along one or both edges of thestrip, so that the strip could be severed to provide pieces of frontplane laminate suitable for individual displays and each having at leastone tab. Alternatively, the conductive layer could have the form of asimple strip without tabs, and the electro-optic medium be coated in theform of a strip narrower than the strip of conductive material, thusleaving one or both edges of the conductive material exposed to provideconnection areas which can contact the backplane when the front planelaminate is laminated thereto.

FIG. 22 illustrates a process similar to that of FIG. 21 but in whichthe electro-optic medium is applied as a series of patches 930 ratherthan as a continuous strip, with each patch 930 being used for onedisplay. A modification of the process of FIG. 22 may be used to providea front plane laminate suitable for use with the true underfill seal ofFIG. 14. If the conductive layer is modified to extend over the wholesurface of the web 922 of substrate material and the electro-opticmedium is coated as appropriately-sized patches 930, severing the web922 between adjacent patches will provide pieces of front plane laminatein which the substrate and conductive layer extend beyond the peripheryof the layer of electro-optic medium all around the electro-opticmedium, as required for formation of the true underfill seal of FIG. 14.

Optionally, in the process of the present invention, after lamination ofthe front plane laminate to the backplane and before or after formationof the seal (although the latter is typically preferred), the laminatedstructure produced may be autoclaved, that is put into an autoclave,which is a controlled environment chamber where the temperature andpressure can be increased to bake the structure. Such autoclavingfacilitates the removal of small air voids in the laminated structure byforcing them out via heating. Alternatively, removal of voids may beeffected by performing the lamination of the front plane laminate to thebackplane under vacuum.

The process of the present invention can greatly simplify themanufacture of electro-optic displays and increases the throughput of adisplay manufacturing process by reducing the number of steps andmaterials required compared with conventional display manufacturingtechniques, thus significantly reducing the cost of manufacturing suchdisplays.

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention. For example, the electrostatic chuck 42 shown in FIG. 4 couldbe replaced be a vacuum chuck, although a vacuum chuck does have thedisadvantage of visible vacuum holes that would make detection ofdefects near the holes more difficult, and consequently it wouldprobably be necessary to test each sheet of laminate twice in differentpositions on the chuck in order to detect defects that would be obscuredby the vacuum holes in one position. Similarly, the line scan camera 52could be replaced by a matrix camera and focusing optics. Accordingly,the foregoing description is to be construed in an illustrative and notin a limitative sense.

1. A process for forming an electro-optic display comprising: providinga backplane comprising at least one pixel electrode; providing a frontsub-assembly comprising, in order, an adhesive layer, a layer ofelectro-optic material and at least one support layer, the support layerbeing larger than the layer of electro-optic material and the adhesivelayer so as to leave a peripheral area of the support layer exposedaround the layer of electro-optic material; dispensing a curablematerial on to one of the backplane and the peripheral area of thesupport member, and curing the curable material to form a dam member;laminating the adhesive layer of the front sub-assembly to thebackplane, and thereby causing the dam member to extend between thebackplane and the peripheral area of the support layer; and dispensing asealing material adjacent the dam member to form a seal extendingbetween the backplane and the peripheral area of the support layer.
 2. Aprocess according to claim 1 wherein the curable material is dispensedand cured to form two dam members spaced from each other, and thesealing material is dispensed between the two dam members.
 3. A processaccording to claim 1 wherein the electro-optic medium comprises anelectrophoretic medium.
 4. A process according to claim 3 wherein theelectrophoretic medium comprises an encapsulated electrophoretic medium.5. A process according to claim 3 wherein the electrophoretic mediumcomprises electrically charged particles and a fluid present as aplurality of discrete droplets surrounded by a continuous phasecomprising a polymeric material.
 6. A process according to claim 3wherein the electrophoretic medium comprises a microcell electrophoreticmedium.
 7. A method of testing an electro-optic medium, the methodcomprising: disposing a layer of the electro-optic medium on alight-transmissive first electrically-conductive layer; disposing asecond electrically-conductive layer on the opposed side of the layer ofelectro-optic medium from the first electrically-conductive layer;applying a potential difference between the first and secondelectrically-conductive layers, thereby forming an image on the medium;and observing the image thus formed.
 8. A method according to claim 7wherein the electro-optic medium comprises an electrophoretic medium. 9.A method according to claim 8 wherein the electrophoretic mediumcomprises an encapsulated electrophoretic medium.
 10. A method accordingto claim 8 wherein the electrophoretic medium comprises electricallycharged particles and a fluid present as a plurality of discretedroplets surrounded by a continuous phase comprising a polymericmaterial.
 11. A method according to claim 8 wherein the electrophoreticmedium comprises a microcell electrophoretic medium.
 12. A method oftesting an electro-optic medium, the method comprising: disposing alayer of the electro-optic medium on a light-transmissiveelectrically-conductive layer; disposing a release on the opposed sideof the layer of electro-optic medium from the electrically-conductivelayer; placing an electrostatic charge on the release sheet, therebyforming an image on the medium; and observing the image thus formed. 13.A method according to claim 12 wherein the electro-optic mediumcomprises an electrophoretic medium.
 14. A method according to claim 13wherein the electrophoretic medium comprises an encapsulatedelectrophoretic medium.
 15. A method according to claim 13 wherein theelectrophoretic medium comprises electrically charged particles and afluid present as a plurality of discrete droplets surrounded by acontinuous phase comprising a polymeric material.
 16. A method accordingto claim 13 wherein the electrophoretic medium comprises a microcellelectrophoretic medium.
 17. A method of forming a sub-assembly useful inthe production of an electro-optic display, the method comprising:forming a layer of a solid electro-optic medium; and coating a layer ofan adhesive on to the layer of solid electro-optic medium.
 18. A methodaccording to claim 17 wherein the layer of solid electro-optic medium isformed on a release sheet.
 19. A method according to claim 17 whereinthe layer of solid electro-optic medium is formed on alight-transmissive electrically-conductive layer.
 20. A method accordingto claim 17 further comprising forming a second layer of adhesive on theopposed side of the layer of solid electro-optic medium from thepreviously coated layer of adhesive.
 21. A method according to claim 17further comprising contacting the layer of adhesive with a backplanecomprising at least one electrode.
 22. A method according to claim 17further comprising contacting the layer of adhesive with alight-transmissive electrode.
 23. A method according to claim 20 furthercomprising contacting one of the adhesive layers with a backplane andthe other adhesive layer with a light-transmissive electrode.
 24. Amethod according to claim 17 further comprising placing a release sheetover the exposed surface of the layer of adhesive.
 25. A methodaccording to claim 20 further comprising placing release sheets overboth the adhesive layers.
 26. A method according to claim 17 wherein theelectro-optic medium comprises an electrophoretic medium.
 27. A methodaccording to claim 26 wherein the electrophoretic medium comprises anencapsulated electrophoretic medium.
 28. A method according to claim 26wherein the electrophoretic medium comprises electrically chargedparticles and a fluid present as a plurality of discrete dropletssurrounded by a continuous phase comprising a polymeric material.
 29. Amethod according to claim 26 wherein the electrophoretic mediumcomprises a microcell electrophoretic medium.